Core C is the animal core and provides essential services to all projects in the PPG. It provides access for PPG members to complex mouse genetic models of breast cancer and allows genetic investigation into the mechanisms of tumor progression and metastasis. The core has pioneered the lineage labeling of particular cell types and'has been essential to many of the major findings of the PPG, especially those involving macrophage-tumor cell interactions. In the next granting period, models of breast cancer will be maintained with lineage marked cells in order to study complex behaviors after genetic manipulation in vivo. The core has also developed lineages marked with photo-switchable fluorescent proteins that will be essential to fate mapping of macrophages and tumor cells in the next funding period. The Core has also developed novel macrophage restricted cre recombinases both constitutive and inducible, as well as new more efficient and restricted mammary epithelial specific cres. The core will also develop new methodologies with novel fluorescent proteins and lineage tracing methods during the next granting period.